What is it?

Flaxseed is the seed from the plant Linum usitatissimum. Oil from the seed is used to make medicine.

People try flaxseed oil for many different conditions, including rheumatoid arthritis and high cholesterol. It is also tried for treating osteoarthritis, anxiety, benign prostatic hyperplasia (BPH), vaginal infections, dry eyes, “hardening of the arteries” (atherosclerosis), high blood pressure, heart disease, diabetes, and attention deficit-hyperactivity disorder (ADHD).

Some people use flaxseed oil as a laxative for constipation, for weight loss, and to prevent breast cancer and prostate cancer.

Flaxseed oil is also applied to the skin to sooth irritations or soften roughness.

In foods, flaxseed oil is used as cooking oil and in margarines.

In manufacturing, flaxseed oil is used as an ingredient in paints, varnishes, linoleum, and soap; and as a waterproofing agent.

Possibly ineffective for...

Bipolar disorder. Research suggests that taking flaxseed oil daily for 16 weeks does not improve symptoms of mania or depression in children with bipolar disorder.

Diabetes. Research suggests that flaxseed oil does not lower blood sugar or improve insulin levels in people with type 2 diabetes.

High cholesterol. Early research suggests that taking flaxseed oil daily for 3 months lowers total cholesterol in people with high cholesterol. However, this early research is not reliable. More high-quality evidence suggests that flaxseed oil does not reduce cholesterol levels in people with high cholesterol and high triglycerides.

Rheumatoid arthritis (RA). Taking flaxseed oil daily for 3 months does not seem to improve symptoms of pain and stiffness, and has no effect on laboratory tests that measure the severity of RA.

Insufficient evidence to rate effectiveness for...

Attention deficit-hyperactivity disorder (ADHD). There is some evidence that taking flaxseed oil might improve attention, impulsiveness, restlessness, and self-control in children with ADHD.

"Hardening of the arteries" (atherosclerosis). There is some evidence that increasing the amount of linolenic acid in the diet can help to prevent hardening of the arteries. Flaxseed oil contains linolenic acid, and therefore some people suggest that flaxseed oil might prevent atherosclerosis. Though this assumption seems reasonable, there has been no research yet to prove it is correct.

Breast cancer. Women who have higher levels of alpha-linolenic acid in their breast tissue seem to be less likely to get breast cancer. Scientists think that high intake of linolenic acid might protect against breast cancer. Flaxseed oil is one source of linolenic acid. However it is not known if increasing flaxseed oil intake will help to prevent breast cancer.

Heart disease. . People with existing heart disease who consume more alpha-linolenic acid in their diet seem to have a lower risk of dying from heart disease. Flaxseed oil is one source of alpha-linolenic acid. However, research has not directly measured the effect of flaxseed oil intake on heart disease outcomes. It is also not known if flaxseed oil supplements have the same effects as flaxseed oil from food.

Dry skin. There is inconsistent evidence about the effects of flaxseed oil for dry skin. Some research suggests that taking flaxseed oil by mouth with alpha-tocopherol daily for 12 weeks does not improve skin moisture in women with dry skin. However, other research suggests that taking flaxseed oil by mouth for the same length of time can improve skin moisture and roughness.

Exercise performance. Lower-quality research suggests that alpha-linolenic acid, a chemical in flaxseed oil, does not improve muscle strength in older adults.

HIV. Early research suggests that taking a formula containing arginine, yeast RNA, and alpha-linolenic acid, a chemical in flaxseed oil, improves weight gain, but not immune function in people with HIV.

High blood pressure. Early studies suggest that flaxseed oil supplements help to lower blood pressure in men with normal blood pressure, but high cholesterol. It is not clear if flaxseed oil lowers blood pressure in people with high blood pressure.

An ovary disorder known as polycystic ovary syndrome (PCOS). Research suggests that taking flaxseed oil for 6 weeks might lower triglyceride levels, but does not affect weight, blood sugar, or cholesterol levels in women with PCOS.

Pneumonia. Consuming alpha-linolenic acid in the diet seem to be linked to a reduced risk of developing pneumonia. Flaxseed oil is one source of alpha-linolenic acid. However, research has not directly measured the effect of flaxseed oil intake on pneumonia outcomes. It is also not known if flaxseed oil supplements have the same effects as flaxseed oil from food.

Prostate cancer. Research is inconsistent on the effect of the flaxseed oil ingredient, alpha-linolenic acid, in prostate cancer. Some research suggests that high dietary intake of alpha-linolenic acid is linked with an increased risk for prostate cancer. Other research suggests high intake or high blood levels of alpha-linolenic acid is not linked with the overall risk of prostate cancer; however, extra alpha-linolenic acid might make existing prostate cancer worse. The source of alpha-linolenic acid appears to be important. Alpha-linolenic acid from dairy and meat sources has been positively linked with prostate cancer. Alpha-linolenic acid from plant sources, such as flaxseed or flaxseed oil, does not affect prostate cancer risk.

Anxiety.

Constipation.

Cancer.

Vaginal problems.

Weight loss.

Other conditions.

More evidence is needed to rate flaxseed oil for these uses.

How does it work?

Flaxseed oil is a source of polyunsaturated fatty acids such as alpha-linolenic acid. The alpha-linolenic acid and related chemicals in flaxseed oil seem to decrease inflammation. That is why flaxseed oil is thought to be useful for rheumatoid arthritis and other inflammatory (swelling) diseases.

Are there safety concerns?

Flaxseed oil is LIKELY SAFE for most adults when taken by mouth appropriately short-term.

Large doses of 30 grams per day and higher can cause loose stools and diarrhea. Allergic reactions have occurred while taking flaxseed oil.

Some men worry that taking flaxseed oil might increase their chance of getting prostate cancer because of the alpha-linolenic acid that flaxseed oil contains. Researchers are still trying to figure out the role of alpha-linolenic acid in prostate cancer. Some studies suggest that alpha-linolenic acid may increase risk or make existing prostate cancer worse, but other studies find no connection. Nevertheless, the alpha-linolenic acid in flaxseed oil does not seem to be a problem. Alpha-linolenic acid from plant sources, such as flaxseed, does not seem to affect prostate cancer risk, although alpha-linolenic acid from dairy and meat sources has been linked in some studies with prostate cancer.

Not enough is known about the safety of flaxseed oil when it is applied to the skin.

Special precautions & warnings:

Pregnancy: Flaxseed oil is POSSIBLY UNSAFE when taken by mouth during pregnancy. Some research suggests that flaxseed oil might increase the chance of premature birth when taken during the second or third trimesters of pregnancy. However, other research suggests that taking flaxseed oil might be safe starting from the second or third trimester and continuing until delivery. Until more is known, pregnant women should avoid taking flaxseed oil.

Children: Flaxseed is POSSIBLY SAFE for children when taken by mouth, short-term.

Breast-feeding: There isn’t enough reliable information available about the safety of flaxseed oil during breast-feeding. Stay on the safe side and avoid using flaxseed oil while breast-feeding until more is known.

Bleeding disorders: Flaxseed oil might increase the risk of severe bleeding in patients with bleeding disorders. Talk to your healthcare provider before using flaxseed oil if you have a bleeding disorder.

Surgery: Flaxseed oil might increase the risk of bleeding during and after surgery. Stop using it at least 2 weeks before a scheduled surgery.

Flaxseed oil can increase the amount of time it takes for blood to clot. Taking it along with other herbs and supplements that slow blood clotting can slow blood clotting even more and could increase the risk of bleeding and bruising in some people. Some of these herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, and others.

Are there interactions with foods?

There are no known interactions with foods.

What dose is used?

The appropriate dose of flaxseed oil depends on several factors such as the user’s age, health, and several other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for flaxseed oil. Keep in mind that natural products are not always necessarily safe and dosages can be important. Be sure to follow relevant directions on product labels and consult your pharmacist or physician or other healthcare professional before using.

Note that flaxseed oil can easily break down chemically if exposed to light, heat, or air. Flaxseed oil should be stored in a frosted bottle and protected from heat. It can be stored in the refrigerator.

University of Montreal. Pregnant Women Consuming Flaxseed Oil Have High Risk Of Premature Birth.ScienceDaily, October 29, 2008. Available at: www.sciencedaily.com/releases/2008/10/081027140817.htm (Accessed May 14, 2009).

This copyrighted, evidence-based medicine resource is provided by Natural Medicines Comprehensive Database Consumer Version. Natural Medicines Comprehensive Database disclaims any responsibility related to consequences of using any product. This monograph should not replace advice from a healthcare professional and should not be used for the diagnosis or treatment of any medical condition.